Various embodiments of the present invention relate generally to a semiconductor memory device and methods of operating the same.
Semiconductor memory is a memory device comprising of semiconductor materials, such as silicon (Si), germanium (Ge), gallium arsenide (GaAs), and indium phosphide (InP), and chiefly divided into volatile and nonvolatile types.
Volatile memory is a memory device in which data stored therein is lost when the supply of power is blocked. Different types of volatile memory include static RAM (SRAM), dynamic RAM (DRAM), and synchronous DRAM (SDRAM). Nonvolatile memory is a memory device that retains data stored therein even when the supply of power is blocked. Different types of nonvolatile memory includes ROM (Read Only Memory), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable and programmable ROM (EEPROM), flash memory, phase-change RAM (PRAM), magnetic RAM (MRAM), resistive RAM (RRAM), and ferroelectric RAM (FRAM). Flash memory is chiefly divided into NOR and NAND types.
The memory cell of a semiconductor memory device, such as flash memory, is supplied with high voltage when a program operation and an erase operation are performed. The memory cell of the semiconductor memory device gradually deteriorates as the program/erase cycle increases, at which the threshold voltage of the memory cell rises even though data stored remains unchanged. This lowers the reliability of the semiconductor memory device.